This invention relates to the operation of the valves of an internal combustion engine, particularly control of the phase angles at which the valves open and close.
It is generally known that improvements in engine operation are attainable by modulation of the phase angles at which engine valves open and close. Such control is applicable to both the intake and exhaust valves although for any of a number of different reasons the control of only one type of valves may be implimented in a given engine.
One known means for effectuating valve control is by employing a "lost-motion" type actuator between a camshaft and each valve. Since the throw of each lobe of the camshaft is fixed, the camshaft will open and close each valve at fixed opening and closing phase angles if there is no lost-motion in the mechanisms between the lobes and the valves. The inclusion of a lost-motion actuator in the mechanism between the camshaft and each valve allows some of the motion that is generated by the camshaft to be taken up by the actuator with the result that the opening phase angle of the valve can be retarded and the closing phase angle advanced from the fixed phase angles that would otherwise exist in the absence of the lost-motion.
U.S. Pats. 4,615,306 and 4,796,573 disclose lost-motion valve control systems in which the lost-motion actuators are extended and contracted in length by the introduction and exhaustion of hydraulic fluid. The engine's lubrication system is used as the source of hydraulic fluid with the fluid being engine lubricant, i.e. oil. The oil that is discharged from one actuator is routed to a common gallery for recovery and subsequent use by other actuators so that the load on the engine's lubrication system is kept to a minimum. In order to keep cost low, previous systems such as that of U.S. Pat. 4,615,306 have employed solenoid valves shared by actuators and using a system of check valves to insure that the solenoid has control of each valve as it becomes active.
As an actuator contracts, the hydraulic pressure pulse that it generates can contribute to expanding an inactive actuator so that high response rates can be achieved. If an actuator can be kept in contact with the valvetrain at all times, the response rate can be as high as the cycle rate of the camshaft. Moreover, by keeping an actuator in contact with the valvetrain at all times, durability issues arising from impacting of parts against each other are essentially eliminated.
Previous systems with shared solenoids have used the pressure pulse from a contracting actuator for actuator re-extension, but the timing of the pressure pulse was not under the control of the solenoid since refilling was done through the check valves.
The present invention contemplates the use of a solenoid valve as the sole fluid path to and from an actuator so that timing of the refilling part of the cycle can be controlled by the ECU (engine electronic control unit). The solenoid valve control envisioned by the invention can also be used to prevent a pressure pulse from entering an already expanded actuator, which might allow the engine valve to be momentarily lifted from its seat thereby possibly causing cylinder leakage and/or valve or valve seat damage.
Since the pressure pulses in an engine with a small number of cylinders may not overlap with the refill time in adjacent cylinders, particularly at low engine speeds, some means of storing pressurized hydraulic fluid is desirable. An accumulator connected to the gallery that is common to all solenoid valve outlets can store the fluid until the time is right to refill an actuator. In this way, with all solenoid valves closed and the check valve back to the lubrication system closed, pressurized fluid is trapped until one of the solenoid valves opens. Previous systems (U.S. Pat. 4,671,221) used accumulators for such purposes, but were costly because they had one accumulator per engine valve and lacked solenoid control of the refill cycle since there was a check valve path from the accumulator back to the actuator.
Other advantages of the invention include the elimination of multiple check valves, with some reliability benefits in the reduction of leakage paths and the elimination of possible wear points. The individual solenoids are also vastly more consistent and repeatable than ordinary check valves, and of much higher response time. While it might be possible to design check valves that might be repeatable, fast, and reliable enough, it seems that their cost would likely exceed that of the solenoid valves.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims, which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention in accordance with the best mode contemplated at the present time in carrying out the invention.